P0406
Exhaust Gas Recirculation Sensor A Circuit High
Encountering the engine check light code P0406 signifies an explicit mechanical or electrical operational breakdown categorized as "Exhaust Gas Recirculation Sensor A Circuit High". Professional scanner tools usually flag this subsystem loop early on.
Driver's Summary
When your OBD2 scanner shows P0406, the engine control module has flagged an issue specifically related to exhaust gas recirculation sensor a circuit high. Typical symptoms include engine stalling, hesitation, rough idle, poor performance. Short trips are generally acceptable, but avoid high-load driving and get this inspected soon.
Symptoms
Engine stalling, hesitation, rough idle, poor performance
Common Causes
- Short to voltage in EGR sensor circuit
- Failed EGR position sensor
- EGR valve stuck open due to carbon
- Poor ground connection
How to Fix
- 1 Repair short to battery voltage
- 2 Replace EGR valve/sensor assembly
- 3 Clean carbon from EGR valve
- 4 Fix ground wire
Technical Explanation
Code P0406 is confirmed when the ECM's diagnostic algorithm detects a parameter deviation that persists across a defined number of consecutive drive cycles. EGR flow is verified by monitoring changes in MAP sensor readings before and after valve actuation; correct EGR flow produces a predictable pressure drop in the intake manifold that the ECM can measure with precision. The MIL illuminates after the fault is confirmed on two consecutive drive cycles, and the freeze frame data captured at first detection is stored in the PCM's memory for diagnostic reference.
Is It Safe to Drive?
While the vehicle is typically drivable with P0406 active, avoid towing, aggressive acceleration, or extended highway driving until the fault is resolved. The primary risk is accelerated wear on short to voltage in egr sensor circuit and failed egr position sensor.
Mechanic's Pro Tip
For P0406, test the solenoid's coil resistance with a multimeter before ordering parts — most solenoids should read between 14 and 40 ohms; an open (infinite resistance) or short (near zero) confirms it's failed electrically. Also verify the PCM is commanding the solenoid by backprobing the connector with a test light during the relevant operating condition — if there's no command signal, the fault is in the PCM or wiring, not the solenoid itself.
EGR cleaning: $80; EGR Replacement: $200 - $350